1. Field of the Invention
The present invention relates to a powder conveying device for conveying toner or similar powder from a powder storing portion to a destination positioned below the powder storing portion via a pipe, and an image forming apparatus using the same.
2. Description of the Prior Art
It is a common practice with a copier, facsimile apparatus, printer or similar image forming apparatus to use a toner conveying device. The toner conveying device includes toner discharging means for discharging toner from a toner container and a pipe connecting the toner container to a developing device configured to develop a latent image formed on a photoconductive drum or similar image carrier with the toner. The toner discharging means is operated to discharge the toner from the toner container to the pipe for thereby directly conveying the toner to the developing device, as needed. If the toner container is positioned at a lower level or height than the developing device, then the toner or powder, introduced into the pipe must be lifted toward the developing device against gravity, resulting in low conveying efficiency and the stop-up of the pipe
In light of the above, the toner container is usually positioned at a higher level than the developing device such that the toner is conveyed in the direction of gravity. Japanese Patent Laid-Open Publication No. 8-30097, for example, discloses a toner conveying device configured to causes toner, which is discharged from a toner box or toner container to a pipe by toner discharging means, to drop into a developing device due to its own weight.
However, the toner conveying device taught in the above document has a problem that when the toner, introduced into the pipe, accumulates on the inner wall of the pipe in a certain amount, the toner is apt to rush into the developing device at a time. In a developing system using a two-component type developer, i.e., a toner and magnetic carrier mixture, the toner rushed into the developing device makes it difficult to accurately control the toner content of the developer. On the other hand, in a developing system using a single-component type developer, i.e., toner, the above toner causes the ratio of toner not sufficiently charged to sharply increase in the developing device, resulting in background contamination. If the toner box and developing device are positioned close to each other in order to reduce the length of the pipe as far as possible, then the toner can be prevented from accumulating in the pipe and rushing into the developing device. This, however, obstructs the free layout of various devices in the image forming apparatus.
An arrangement may be made such that the toner discharged from the toner container does not drop from the pipe due to its own weight, but stays in the pipe while being conveyed toward the developing device in an amount controllable on the basis of the amount of drive of a conveying member disposed in the pipe. Such an arrangement still has a problem that when some impact acts on the pipe, the toner in the pipe is apt to rush into the developing device at a time even when the conveying member is not driven.
The problems described above in relation to toner are also apt to arise in any other powder conveying device dealing with powder other than toner.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-335024, 10-133464, 10-239969, 10-239974 and 11-231631.